Insulation



Jam 8, 1952 J. s. JOHNSON ET A1. 2,581,862

INSULATION Filed Sept. 14, 1944 INVENTORS .fob/7 5 Jabnfon and Patented Jan. 8, 1952 INSULATION John S. Johnson, Verona, and Earl L. Schulman,

Wilkinsburg, Pa., assignora, by meme araignments, to the United States of America as represented by the United States Atomlc'Energy Commission Application September 14, 1944, Serial No. 554,080

1 Claim. (Cl. 171-252) Our invention relates to electrical insulation. and it has particular relation to the insulation of small-sized single conductors which are relatively long and which are inserted into slots in the magnetizable core of a dynamo-electric machine or other electrical apparatus.

While our invention is susceptible of many other uses, it is particularly adapted to the problem of insulating the coil-sides of motor-windings made of very thin strap-conductors of ribbon-like configuration, such as a conductor having a cross-section less than of an inch by 1/2 of an inch.

Heretofore, it has been customary to insulate such coil-sides with a fish-paper slot-wrapper, the edges of which are overlapped at the top of the coil-side. When the coil-side or conductor is very thin, it is very diiilcult to keep these top overlapped liner-edges in place, with the result that the insulation has frequently been damaged in winding, sometimes necessitating the removal of a number of undamaged coils in order to replace a single damaged coil-side.

An object of our present invention is to overcome the foregoing and other diiiiculties by producing a molded insulation of highly consolidated class B material, having high dielectric strength, good mechanical properties such as toughness and ability to withstand winding-abuse, good thermal stability, good arc-resistance, and a novel method of application.

A further object of our invention is to provide a tubular member, made in one integral piece, composed of initially soft, circumierentially wound, impregnable sheet material having a dimension in an axial direction substantially equal to the axial length of the nished tubular member, and an impregnating binder of a thermosetting material.

A more specinc object is to provide a molded tubular member composed of a butt-jointed layer of a circumferentially wound wrapper-material, and a compressed impregnating binder of a hardenable material, preferably thermosetting. The wrapper-material may also be lap-jointed, and it may be in as many layers as may be necessary, in order to build up the desired thickness.

A still further object of our invention is to provide a newcombination making it feasible to use a molded member which is composed of a thermosetting material which is capable, during thermosetting, of strongly attacking the usual forms of flbrous carbohydrates, and utilizing such binding material to bind a brous filler which is resistant to attacks of said Y. binding material during and after the thermosetting action.

A still further object of our invention is to provide a motor or other electrical apparatus, having a slotted magnetizable core, carrying a winding having two coil-side portions lying in each slot, with at sides adjacent to each other, each coil-side portion having an adherent butt- ;lointed layer of insulating material wound circumterentially around the coil-side portion, with the butt-joints of each pair of coil-side portions in any slot disposed in staggered relation to each other in said adjacent ilat sides of the pair of coil-side portions. In this way, the insulationjoints are removed from the grounded coreportions of the machine, and they are staggered with relation to each other, so as to increase the creepage-insulation leakage-distance between the two conductors lying in the same slot of the core.

With the foregoing and other objects in view. our invention consists in the structures, parts, combinations, apparatus, systems and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

Figure 1 is a longitudinal sectional view of a motor embodying our invention;

Fig. 2 is an enlarged cross-sectional view of a portion of the stator-core showing a slot with two of our coil-sides in place;

Fig. 3 is an enlarged view of a coil-side or conductor, showing a modiiied manner of wrapping the insulation; and

Fig. 4 is a somewhat diagrammatic view of a mold which is utilized to compress the insulation prior to, and during the thermosetting operation, and it also shows an end view of a conductor having a preferred form of wrapper in the form of a single lap-jointed layer of impregnated insulating material.

As indicated in Fig. 1, our invention is applicable to electrical apparatus such as a motor having a slotted stator-core 5, and a slotted rotor-core C, having an annular air-gap l in-between. The

3 rotor-core 6 is carried by suitably journalled shaft l. The rotor-core 8 is provided with any suitable type of induction-motor winding, such as a squirrel-cage winding 9.

The stator-core carries a primary winding II which constitutes the subject-matter of our present invention. It has a number of coils or turns. having straight coil-sideportions i2. lyiner in the slots of the core 5. and having bent endturn portions I3. As shown in Fig. 2, each stator slot Il has two coil-side portions i2 and I2 therein. lying side by side in the slot. each with its own insulating wrapper I5. The winding III is composed of insulated strap-conductors i2.

I2', each pair of coil-sides, which lie in any one slot, having their flat sides adjacent to each other.

In the form of embodiment of our invention shown in Fig. 2, the insulating wrapper i5 which surrounds each individual coil-side is composed of a single butt-jointed layer of an initially7 soft. impregnated, insulating sheet-material. preferably non-ferrous asbestos paper. -which is wrapped clrcumferentially around the substantially straight coil-side I2 which it covers. The

widthlof this insulating wrapper is enual to the desired length of the finished insulating cell or tubular member surrounding the straight coilsidev portion I2 which lies in a. stator-slot Iii. extending somewhat beyond the stator-core 5 at each end thereof. The two butt-joints I6 of the two insulating cells i5 which cover the two coil-sides I2 .and I2' in any slot are disposed in the adjacent or abutting flat faces or sides oi the two lconductors lying. in the slot, and the two butt-joints I6 are staggered with relation to each other, so as to provide a good .creepage-distance between each other and also between each butt- ;Ioint and the grounded portions of the machine. The two insulated coil-sides i2 and I2 of the winding. which lie in any stator-slot it. are held in. place by means of a slot-wedge il, as shown in Fig. 2. ,Either before or after being wrapped around its coil-side I2, each insulating asbestos-paper wrapper Il is impregnated with a synthetic resin or other hardenable binding-material. preferably thermosetting. The'resin Imay be a copolymer of propyleneglycol-maleate andl styrene. This material is a thermosetting materiahthat is, one which permanently changes fromv a liquid condition to a' hard lsolid;4 when subjected, for a brief.4 time. to a suitably elevated temperature. the material being thereupon capable of being heated to the same temperature. or even to high temperatures, without materially softening again. The particular resin which we prefer is initially so Afluid (substantially like water) that it can freduently be utilized without a solvent. which facilitates the production of a' .relativelyy voidfree, well-consolidated. insulation-wall.

*Because this resin-materialis also one which is zpap'able of strongly'attackingthe usual forms of fibrous carbohydrates, such as wood-pulp paper. and cotton. or-silk clothrorother cellulosic materials,4 particularly during; the elevated temperature-conditions of the -thermosetting lopera tion. it is quite desirable either to altogether avoid the useof eellulosic materials in theimpregnated insulating wrapper, or at least to utilize a wrapper in which the major portion, or a sufficient portion, :of its constituency, is composed of non-cellulosic-or inorganic fibersorabsorbent material;

Instead-,of utilizing a singles-'layer insulating wrapper "i5 or tube around eachl straight coil-side I2, as shown in Fig. 2, we may utilize a plurality of layers of lap-jointed impregnated sheet-material, as shown at I5' in Fig. 3.

Preferably. however, in the particular applica'- tion for which our invention was primarily designed, we utilize a single insulating layer, but with overlapping or lap-jointed ends I8, as shown in Fig. 4, in which case no care needs to be taken concerning the precise circumferential extent of the wrapper, or the precise amount of overlap, or the position of the overlapped joints, with respect to staggering, because in the finished product, the joints are pressed out and have as great insulating and mechanical strength as any other portio/n of the insulating cell.

Whatever may be the precise manner of wrapping the/insulating cell around the straight coilside portion i2, the wrapped coil-side portion, after/wrapping and impregnation, is placed in a moldy 50, Fig. 4, and set up under heat and pressure. This causes the initially soft wrappingmaterial to be compressed, while causing the polymerlzin binding-resin to convert itself into a solid, inte al mass, which is tightly adherent to the asbestos fibers, and also tightly coherent within its own particles, so that it has good mechanical properties, such as toughness and ability to withstand winding-abuse better than conventional coil-coverings.

The insulation thus produced is at least equal to class B insulation, which, according to AIEE standards, must be able to continuously withstand a hot-spot temperature of C. In general, we may say that our insulation will continuously withstand a temperature higher than 125 C. This applies both to the asbestos paper and the thermosetting impregnating bindingmaterial. The insulation is highly consolidated, and it has a high dielectric strength, so that a large percentage of the slot-area can be usefully utilized for the copper conductor of the wire or strap I2 which is utilized for the winding II.

The electrical properties of the finished insulating material may be summarized as follows. Its short-time dielectric strength is 450 volts per mil. Its step-by-step dielectric strength is 300 volts per mil. Its arc-resistance, by A. S. T. M. standards, is seconds. The material does not track.

While we prefer to utilize the particular resin which has previously been named, we are not limited to this particular resin. We are not even` limited to a resin having an acid val-ue of 50 or more, such as we prefer, referringr to the number of milligrams o f KOH necessary to neutralize each gram of the sample. It is believed to be mainly this acidity which causes the ilmpregnating' thermosetting material to be destructive to cellulosic4 fibers. Other thermosetting resins whichl might be utilized include the general class of` alkyd resins dissolved in a vinylhfcorripoundf which include combinations vof a polyh'ydr'ic"'alf-` coholan unsaturated dibasic' acid, and a vinyl compound, or, in general, most or all of the resinous reaction-products of organic acids, as

well' as other haidenablelimpregnating agents;A

which could also be utilized. A We claim as our invention:

An electrical apparatus having a SlottedA mag-' netizable core and a winding having two straight coil-side portions lying side by side in eachv slot- With flat sides adjacent to each other, leach coil` side portion having an adherent "butt-jointed layer of non-ferrousasbestosv paper wound 'cir-- s. cumferentially around the coil-side portion and impregnated with a thermosetting resin consisting essentially of a copolymer of propylene glycolmaleate and styrene, said layer having a dimension in an axial direction substantially equal 5 to the axial length of its straight coil-side portion, and with the butt-joints of each pair of coil-side portions in any slot disposed in staggered relation to each other in said adjacent flat sides of the pair of coil-side portions. 10

JCHN S. JOHNSON.

EARL L. SCHULMAN.

REFERENCES CITED The following references are of record in the 16 ie of this patent:

UNITED STATES PATENTS Number Name Date Johns Jr. June 11, 1889 Baekeland May 5, 1912 Field Aug. 17, 1915 Apple Apr. 23, 1918 Reid Oct. 27, 1931 Apple Feb. 14, 1933 Ellis Sept. 9, 1941 Rochow Oct. 7, 1941 Patterson et al. Dec. 28, 1943 Keyes Feb. 20, 1945 Schulman Nov. 16, 1948 

